1. Field of the invention
The present invention relates generally to polymeric implants and, more particularly, to surface metallized polymeric implants so as to improve their biocompatibility, a dry coating method and an apparatus for effecting the metallization.
2. The Prior Art
Fluid replacement and administration of drugs and nutrients by the intravenous route have become an integral part of patient care. It has been estimated that over one-fourth of patients hospitalized in the U.S.A. receive intravenous infusions for one reason or another. The introduction of plastic catheters in 1945 was enthusiastically received for delivering intravenous fluids. Polymers have good bulk properties, such as flexibility. Plastic catheters also are less expensive to make than are steel needles. Hence, many medical device manufacturers prefer using polymeric materials for making implants, such as cannula, needles, catheters, percutaneous connectors and the like. "Cannula" is a general term used in the medical devices field that includes all types of plastic catheters, percutaneous devices, draining tubes and steel needles. The use of polymeric implants, however, has brought with it alarming reports of complications, especially thrombophlebitis and sepsis. See Dennis G. Maki, M.D., et al "Infection Control in Intravenous Therapy," Annals of Internal Medicine 79:867-887, 1973; J. Lewis et al "Assessment of Thromboresistance of Intravenous Cannulae by .sup.125 I-Fibrinogen Scanning," Journal of Biomedical Materials Research, Vol. 19, 99-113 (1985); Mario L. Corona, M.D. et al "Infections Related to Central Venous Catheters," Mayo Clinic Proc. July 1990, Vo. 65.
Some workers in the field have investigated the use and the beneficial effect of an in-line filter in reducing infusion-associated infection, in particular phlebitis, see Kenneth H. Falchuk, M.D., et al "Microparticulate-Induced Phlebitis," The New England Journal of Medicine, Vol. 312, No. 2, Jan. 10, 1985, 78-82. Others have, however, focused on the material of the cannula itself. See Gerald Friedland, M.D., "Infusion-Related Phlebitis--Is the In-Line Filter the Solution? " The New England Journal of Medicine, Vol. 312, No. 2, Jan 10, 1985, 113-115; and John L. Tully, M.D. et al "Complications of Intravenous Therapy with Steel Needles and TEFLON.RTM. Catheters--A Comparative Study," The American Journal of Medicine, Vol. 70, March 1981, 702-706. Amongst others, the latter two articles conclude that steel needles produce fewer infusion-associated complications, such as phlebitis than do plastic cannulae. And therein lies the knob of the problem--how to use advantageously the desirable bulk property of polymeric implants, to wit, flexibility, avoiding infiltration without adversely affecting the patient by exposing him to increased risk of infusion-associated plebitis and infection?
The common assignee herein, Spire Corporation of Bedford, Massachusetts, has been one of the pioneers in the field of ion beam technology. A plasma-supported ion beam technique for coating industrial cutting tools with a thin layer of cubic boron nitride to improve the tools' cutting properties is disclosed in U.S. Pat. No. 4,440,108, of Roger G. Little et al, granted Apr. 3, 1984, and assigned to said Spire Corporation. A plasma-ion deposition process of large-grain, thin semiconductor films directly on low-cost amorphous substrates is disclosed in U.S. Pat. No. 4,443,488, also of Roger G. Little et al, granted Apr. 17, 1984 and assigned to said Spire Corporation. A process of preventing surface discoloration in titanium orthopaedic implants by ion implantation is disclosed in U.S. Pat. No. 4,693,760 of Piran Sioshansi, granted Sep. 15, 1987 and assigned to said Spire Corporation. An ion implantation process for plastics to enhance their surface hardness and their resistance to chemical attack is disclosed in U.S. Pat. No. 4,743,493 of Piran Sioshansi et al, granted May 10, 1988 and assigned to said Spire Corporation. A process for passivating the electrochemically active surface of metal alloys so as to inhibit their corrosion is disclosed in U.S. Pat. No. 4,743,308 of Piran Sloshansi et al, granted May 10, 1988 and assigned to said Spire Corporation. A sputter-enhanced ion implantation process, primarily of ball bearings, without the use of a separate evaporation system is disclosed in U.S. Pat. No. 4,855,026 of Piran Sioshansi, granted Aug. 8, 1989 and assigned to said Spire Corporation. An improved method and apparatus for the uniform ion implantation of spherical surfaces, such as ball bearings, is disclosed in U.S. Pat. No. 4,872,922 of Stephen N. Bunker et al, granted Oct. 10, 1989 and assigned to said Spire Corporation. A method of depositing an ionized cluster on a substrate is disclosed in U.S. Pat. No. 4,152,478 of Toshinori Takagi, granted May 1, 1979. And a method of coating a substrate with a stoichiometric compound is disclosed in U.S. Pat. No. 4,281,029 of Toshinori Takagi et al, granted Jul. 28, 1981. The use of ion beam processing is thus well known and widespread.